1. Field of the Invention
This invention pertains to a new and improved method for the preparation of selectively halogenated ketals and ketones, more specifically selectively chlorinated or brominated ketals and ketones.
2. Description of the Art
Heretofore, it has been extremely difficult to obtain selectively halogenated ketones and ketals. The formation of halogenated ketals has been reported to occur by reaction of halogenated ketones with alcohols in a patent to Morey U.S. Pat. No. 2,374,494, and Dittli et al in Bull. Soc. Chim. Fr. 1968, 4208, by the reaction of vinyl ethers or esters with alkyl hypochlorite as exemplified by Cass U.S. Pat. No. 2,433,890, Weissermel et al German Patent No. 1,053,487, Shostakovskii et al Akad. Nauk SSSR., otdel Khim. Nauk 1953, 1043, and Filachione, U.S. Pat. No. 2,411,826, or by the direct halogenation of ketals, Anselm et al German Pat. No. 639,507, Dusseau et al, Rec. Trav. Chim. Pays-Bas 1970, 535 and Field, J. Am. Chem. Soc. 83, 3504. The first two methods suffer from one or more of the following deficiencies; two step synthesis, use of very low temperatures and low yields. The third method generally suffers from use of inconvenient or relatively expensive reaction systems, e.g. dimethylformamide (DMF) or sulfur dioxide (SO.sub.2) as a solvent, use of metal alcoholates and use of low temperatures.
It is even more difficult to obtain selectively and symmetrically dihalogenated ketones and ketals. This is so because of the natural tendency, once the monohalogenated compound has been formed, of the second halogen to substitute onto the same carbon as the first halogen. Previous attempts to form selective and symmetrical dihalogenated ketones and ketals have usually resulted in the use of excessive amounts of halogenating agents, extreme temperatures and pressures as well as complex equipment. An example of some of the problems encountered by the art is illustrated by Jones, U.S. Pat. No. 2,204,135, however, his solution involves the use of corrosive materials. Rahrs, U.S. Pat. No. 2,235,562, proposed another solution involving chlorinating ketones in the vapor phase and utilizing complex cooling equipment. It can readily be seen that all this is obviated by the instant invention.